One requirement for next-generation wireless communication systems is to be able to support a high data transmission rate. For this purpose, there is ongoing research, such as MIMO (Multiple Input Multiple Output), CoMP (Cooperative Multiple Point Transmission), or relays, but the most fundamental and stable method is to broaden bandwidth.
However, frequency resources are now in saturation, and various technologies are used to occupy a wide range of frequency bands. To meet demand for a higher data transmission and secure a broader bandwidth, the concept of carrier aggregation (CA) has been introduced which ties a number of bands into a single system and provides a design that may satisfy the basic requirement that each spread band may operate an independent system. At this time, the band which enables each independent operation is defined as a component carrier (CC).
To support increasing transmission capacity, recent communication standards, e.g., 3GPP LTE-A or 802.16m, consider expanding the bandwidth up to 20 MHz or more. In such case, one or more component carriers are aggregated to support the broadband. For example, if a single component carrier corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support the maximum of a bandwidth of 20 MHz. As such, the carrier aggregation system uses multiple component carriers, and may be in this sense referred to as a “multi-carrier system”.
In the multi-carrier system, component carriers assigned to a terminal may change for various reasons, such as channel environments or amount of data transmitted. For example, a terminal which is now in communication with two component carriers may be assigned with one more carrier, so that three carriers in total may end up being assigned to the terminal. Or, while communication is underway with three component carriers assigned, one of them may be removed thereby leaving two component carriers assigned. As such, in the case that the component carriers assigned to a terminal vary, mapping between the component carriers and the value in the carrier indication field, which indicates the component carrier may also change. At this time, it needs to be clearly specified how the value in the carrier indication field is mapped with the component carrier.